An electro-optical device incorporating an electrically controllable electro-optical substrate made from a transparent electro-optical material with the optical effect being controlled by applying a voltage between control electrodes is known from German published patent application DE-OS 25 57 254. In that device there is provided on the electro-optical substrate one electrode which is common to all picture points and connected to ground potential, and a plurality of control electrodes, one for each picture point and each capable of being connected to a voltage. In order to be able to achieve a particular electro-optical effect, a predetermined control voltage is required. However, the electro-optical effect is dependent on manufacturing parameters and it is not guaranteed in all cases that similar substrates from different production batches will produce the optimum or a predetermined maximum effect upon application of the same control voltage. Furthermore, as a practical matter, it can easily happen that the control voltage for achieving a certain electro-optical effect must be quite high, e.g., 200 V direct current voltage. Depending on the batch, however, it also happens that the control voltage might have to be adjusted higher or lower in order to achieve consistently the same electro-optical effects. Moreover, for a predetermined light intensity and duration of exposure, the control voltage has to be varied in order to achieve different grey stages.